1. Field of the Invention
This invention relates to an apparatus and process for sensing reflected light patterns for a workpiece in the presence of a welding arc. More particularly, it relates to such an apparatus and process which will discriminate between a reflected light pattern from a workpiece and reflected light from a welding arc. The reflected light patterns are utilized to characterize the workpiece geometry for the purpose of controlling the positioning of the workpiece with respect to a welding head.
2. Description of the Prior Art
Welding head positioning systems are known in the art, in which reflected light projected on the workpiece is sensed in the presence of other reflected light from a welding arc, for the purpose of controlling positioning of the welding head and the workpiece relative to one another. For example T. Nozaki et al, Robot "`Sees`, Decides and Acts", Welding and Metals Fabrication, Vol. 47, No. 9, pp. 647-658 (November, 1979), discloses such a system in which an infrared transmissive filter is used to screen out frequencies of the reflected light at which the reflected projected light and the reflected welding arc light have a similar intensity. While that approach is feasible in the case of a simple spot of light projected on the workpiece, a more complex pattern of light projected on a workpiece requires a better ability to discriminate between projected light and welding arc light. Also, the system does not discriminate against welding sparks, which tend to emit a broad band of light frequencies, including those in which the light source and sensitivity of the camera coincide.